Removal of tramp material from fluid bed vessels

Abstract

A system for removal of tramp or trash material from a single fluidized bed contained within a single vessel used to incinerate or pyrolyze solid fuel, the system comprises a gently sloped, skewed or serpentine stationary bed support and air distributor structure which distributes air in a fashion so as to uniformly fluidize a shallow bed of variable depth across the slope thereof without internally circulating the bed, and at the same time cause non-combustible tramp or trash material (e.g. pieces of steel, rocks, clumps, etc.), to be removed from the bed without passing to a location either above or beneath the bed. The angle of slope is strictly controlled. During periods of non-fluidization and/or non-use, the bed material is kept from falling into the air distribution plenum below the bed support structure by hollow bed containment structure disposed at sites below the bed support structure. Fluidizing air and gravity alone gently walk tramp material downwardly along the top of the bed support structure toward a discharge site. Although the discharge of fluidized air through the grid plate into the bed may be non-vertical, the horizontal component of said air discharge is immediately dissipated and the bed turbulence or direction of fluidization is essentially vertical. The sizing and spacing of air distributor holes may be varied in respect to any sloped grid plate to provide for proper and uniform fluidization across the bed having non-uniform depth without causing rotational mixing within the bed.

What is claimed and desired to be secured by United States Letters Patent is: 
     
       1. A fluidized bed system comprising: a vessel;   stationary flat sloped grid plate means comprising an array of fluidizing apertures disposed in and peripherally connected to the lower portion of the vessel;   a shallow fluid bed resting entirely on the plate means and comprising a variable depth transversely across the vessel, the bed being formed of inert granular material;   means by which fuel particles, containing non-combustible tramp objects, are delivered to the interior of the vessel and to the fluid bed therein;   a source of fluidizing air;   means by which influent fluidizing air is delivered to a site within the vessel below the plate means and the fluid bed;   means at a first elevation above the highest plate means elevation by which influent bed material is delivered to the vessel and the fluid bed within the vessel;   effluent means at a second elevation immediately above the lowest plate means elevation by which effluent bed material and tramp objects exit the fluid bed and the vessel after migrating downwardly along the plate means;   the stationary sloped grid plate means being angularly disposed between the fluid bed and the influent fluidizing air site within the vessel by which the entirety of the bed is uniformly fluidized without internal rotational circulation of the bed while retaining the surface of the bed essentially level, the tramp objects being walked downwardly along the top of the stationary sloped grid plate means to the effluent means solely by gravity and fluidizing air and bed material being prevented from passing through the sloped plate means during both periods of fluidization and non-fluidization.   
     
     
       2. A fluidizing bed system comprising a vessel comprising bed support and fluidizing air distributor structure comprising a relatively flat plate with fluidizing apertures therein and upon which the entire weight of a fluid bed rests, the plate being angularly disposed with respect to the horizontal, at an angle less than the angle of repose of the bed material, the plate being situated within and connected to the vessel whereby fluidizing air is introduced into the bed through said apertures and fuel particles, bed material and tramp material are introduced into the vessel and gravitationally migrate downwardly, bed and tramp materials being selectively discharged from the vessel at a discharge site located above said plate, the system further comprising means below the plate which substantially retain the bed material within the bed above the plate against flow loss thereof through said apertures during times when the bed is not being fluidized. 
     
     
       3. A fluidized bed system according to claim 2 further comprising bed deflector means connected to the plate and projecting upwardly into the bed imparting a circuitous displacement along the top of the air distributor structure to the migration of the bed and tramp materials to the discharge site thereby increasing the dwell time of fuel particles within the bed. 
     
     
       4. A fluidized bed system according to claim 2 wherein the bed support plate, fluidizing air distributor structure and the fluid bed are serpentine in their respective configurations and the fluidization apertures in the plate comprise an array along substantially the entirety of the serpentine plate with the serpentine air distributor structure supplying air to all of the apertures of the serpentine array. 
     
     
       5. A fluidized bed system according to claim 2 wherein the fluidizing air passes through the apertures in the plate in one or more non-vertical directions to augment the gravitational migration of the tramp materials downwardly along the plate toward the discharge site, whereby the fluidization of the bed is uniform and substantially vertical, the non-vertical component of the fluidizing air being essentially dissipated in gently displacing the tramp material down the plate. 
     
     
       6. A fluidized bed system according to claim 2 wherein the apertures in the plate are sized, spaced and distributed to produce at any location within the bed a pressure drop through the apertures of at least 30% of the pressure drop through the bed. 
     
     
       7. A fluidized bed system according to claim 2 wherein the below the plate means comprise bed material catch and collector means carried by and disposed below the plate directly below and juxtaposed each fluidizing aperture into which a very small amount of bed material flows and accumulates immediately upon non-fluidization to thereby promptly clog to prevent further flow and loss of bed material through said fluidizing apertures, the below the plate means further comprising air passageway means by which the bed material earlier clogged in each catch and collector means is returned through the fluidizing apertures to the bed per se under force of fluidizing air upon resumption of fluidization. 
     
     
       8. A fluidizing bed system according to claim 7 wherein the below the plate means collectively comprise a plurality of sections each having a hollow interior exposed to at least one fluidizing aperture, each section being secured to the underside of the plate, and comprising wall means directly and closely juxtaposed each fluidizing aperture. 
     
     
       9. A fluid bed system comprising a single vessel fluidizing air distributor structure comprising helical fluid bed supporting sloped plate means having an upper end and a lower end, with an array of fluidizing apertures disposed in the plate means, the fluidizing air distributor structure and plate means being disposed in the lower part of the vessel, a fluid bed superimposed upon the serpentine sloped plate means and uniformly fluidized, without causing bed circulation, transversely across the entirety of the bed by fluidizing air passing under force through said apertures in the plate means, the helical sloped plate means being connected to the vessel such that the entire bed within the vessel rests thereon, whereby fuel particles, bed material and tramp objects introduced into the vessel gravitationally and pneumatically migrate downwardly along a serpentine flow path, without loss of bed fluidization, as the fuel particles are oxidized within the bed, to and bed material and tramp objects are selectively discharged from the vessel at a discharge site located above the lower end of the helical sloped plate means. 
     
     
       10. A system according to claim 9 further comprising means located below the plate means adjacent each aperture which substantially prevents loss of the bed material from the bed, through the helical sloped plate means during times when the bed is not being fluidized.